Slot coaters and roll coaters are used to apply hot melt adhesives for laminating construction sheet materials, container labels, decorative coverings, and apparel. These and like items serving the industry batch melt materials, deliver to the application point by pressurized heated hoses, apply by heated rolls in a heated bath or manifolds of heated valves and nozzles. The rolls and bath of some roll coaters are heated and maintained at temperature by heated oil. They all experience start up delay required to heat for melting, delivery, and application apparatus. Materials are exposed to a long path and long time at temperature before application. This method necessarily contributes to energy inefficiency and material degradation.
The invention utilizes a perforated sheet steel cylinder susceptor heated by a bar inductor coil to both melt and apply pelletized hot melt adhesive at the application point. Other particle forms of hot melt adhesive such as prills, slats, and chiclets can be applied with the apparatus of the invention. The cylinder susceptor can be fabricated from custom or commercial perforated sheet steel. It can also have an intricate custom pattern etched through a sheet steel cylinder. Bar coil fabrication is well known in the induction heating industry for welded tube seam anneal, heating paper calendaring rolls, and the drying of metal sheet coatings. The length and diameter of the cylinder are chosen to accommodate the size range of substrate to be coated. The amount of high frequency power and rotation speed of the cylinder is adjusted to accommodate the volume of material applied in the process. The process temperature can be controlled by thermocouple wireless transmission or infrared view of the application cylinder.
The apparatus of the invention melts materials within a few seconds at the application point and applies in a pattern or full surface coating. The application cylinder can apply pressure to successive lamination layers. The minor number of components of the invention yields an apparatus of lesser cost. This method of simultaneous melting and application yields superior energy efficiency and start up time.